This invention relates to variable sensitivity biodegradable water washable dye penetrant compositions and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects. The invention is especially concerned with variable sensitivity dye penetrant compositions having the above characteristics, and wherein the sensitivity is controlled simply by incorporation into a basic composition, of additional amounts of the dye vehicle or carrier component of the basic dye penetrant composition, essentially without changing the water washability of the compositions, and employing as vehicle or carrier certain biodegradable nonionic surfactants in the form of certain oxyalkylated alcohols, and mixtures thereof; to a method for preparing such variable sensitivity dye penetrant compositions; and to a method of utilizing such variable sensitivity dye penetrant compositions for non-destructive testing of parts having cracks or defects varying in size from microcracks to gross cracks.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions, such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, dye penetrant compositions are required having varying sensitivity ranging from very high sensitivity, down to medium and low sensitivity.
In addition, it is highly desirable that the various dye penetrant solutions of variable sensitivity be easily formulated and contain a minimum of vehicle or carrier components, and particularly that all of such variable sensitivity dye penetrant compositions have easy water washability from part surfaces without the necessity for carefully balancing a variety of the liquid components which are usually present in prior art dye penetrant solutions, in order to obtain such variable sensitivity and washability control.
Prior art dye penetrant compositions generally consist of various ingredients including in addition to dyes, combinations of solvents such as primary and secondary solvents, wetting agents, often employed in combination, and extenders for controlling the washability of the dye penetrant composition and maintaining its stability in solution. When employing such prior art dye penetrants, in order to obtain different penetrant sensitivities, each formulation of a desired sensitivity requires careful mixing and balancing of the above components. In addition, however, such compositions of varying sensitivity containing the above multiple components generally vary in washability, due to the varying proportions particularly of water insoluble components in such composition.
Thus, in my application Ser. No. 16,804, filed Mar. 5, 1970, abandoned in favor of continuation application Ser. No. 333,494, filed Feb. 20, 1973, now abandoned, there is disclosed production of graded sensitivity dye penetrants employing combinations of dye carriers such as N-methyl-2-pyrrolidone and isobutyl heptyl ketone, together with combinations of soluble and insoluble wetting agents, and wherein a controlled and graded degree of sensitivity for crack detecting is obtained by mixing dye penetrant compositions of these types, each containing different proportions of components, in order to obtain a dye penetrant of a desired sensitivity. Thus, according to such disclosure, two extreme penetrant compositions, that is one of high and the other of low sensitivity are mixed to obtain dry penetrant compositions of intermediate sensitivities. This concept is based on the nature of the dye penetrants employed, which have substantially the same amount of dye for both of the extreme sensitivity formulations noted above, but the resulting compositions of varying sensitivity differ in water solubility and washability characteristics for each formulation.
An additional criterion has recently developed also with respect to dye penetrant solutions and compositions. Generally, dye penetrant solutions presently being used and containing solvents and wetting agents present a disposal problem in that they are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria in sewage disposal plants. Hence, the necessity for the development of dye penetrant solutions and compositions which are biodegradable, that is which employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, has attained considerable importance.
In my above U.S. Pat. Nos. 3,915,885 and 3,915,886 there are disclosed novel dye penetrants which have improved washability and sensitivity characteristics, and which are biodegradable, containing as the vehicle for the dye, certain biodegradable nonionic oxyalkylated alcohols.
Accordingly, an object of the present invention is the provision of variable sensitivity biodegradable water washable dye penetrant compositions which are based on a simple formulation comprised of an essentially single or sole vehicle or carrier for the dye in the form of a biodegradable nonionic surfactant, and which are heat stable, and are essentially non-flammable and non-toxic, and which do not require the use of volatile primary and secondary solvents and couplants, or mixtures thereof. A particular object of the invention is to provide dye penetrant compositions of the above noted type, and wherein the sensitivity of the dye penetrant compositions can be easily controlled simply by addition of predetermined amounts of the above surfactant to the basic dye penetrant, while essentially maintaining the same good washability characteristics for all of the compositions thus obtained, but with varying sensitivity. Still further objects are the provision of procedure for preparing such variable sensitivity water washable and heat stable biodegradable dye penetrant compositions, and procedure employing such compositions for inspection of cracks, flaws and metallurgical conditions in structural components.